Receiver system



ea. 31, 1946. 'H. B. D EAL ET AL I 2,413,2g6

RECEIVER SYSTEM Filed Dec. 20, 1943 T 4 Q... I I

5 Sheets-Sheet 1 OSCAILEATOR I F' M' Y r (zoom 1260 orcLEs) MODULATOR (60 T0 \IO Kc.)

"-7 RELAY 9 6 I 10 I I CARRIER FREQ. F. M. To TRANSMITTER RELAY OSCILLATOR V MULTI- MODULATOR (5 To lo MC) PLIER pUT i (2070mm) OPERATE a 5 SUB- CARRIER CONTROL 14 18 A =1. a a1 5 l l I CARRIER I, E AMPLIFIER. DETECTOR AMDUFER DETECTOR l DETQNATOR D. c. SENSITIVE 29 b AMPLIFIER a L 26 27 as I f RELAY5 I I l SENSITIVE I AMPLIFIER RECT'HER h RELAY INVENTORS HARMON B. DEAL JOHN RANKIN.

WILLIAM .A EXANDER By )1? MAM/- A TTOR/VEV Dec, 31', 1946 H. B. DEAL ET AL 2,413,296

RECEIVER SYSTEM Filed Dec. 20, 1943 5 Sheets-Sheet 2 TRANSFER DIALING 8' TRANSFER 5 N \l J 3 N n m, i- Anr I T' 43 Q :'-i

S INVENTORS m g; HARMON B.DEAL JOHN A. RANKIN BY WILLIAM R.ALEXANDER Dec. 31, 1946.

H. B. DEAL ET AL RECEIVER SYSTEM Filed Dec. 20, 1943 3 Sheets$heet 3 .HIIII- UUCED QMJJOKFZ 00 OF INVENTORS HARMON 8. DEAL JOHN A. RANKIN WILLIAM R.ALEXANDER ATTORNEY Patented Dec. 31,1946

UNITED STATES PATENT OFFICE RECEIVER SYSTEM Harmon 3. Deal, Bloomington, Ind, William R. Alexander, Upper Montclair, N. J and John A. Rankin, Park Ridge, 111., assignors to Radio Corporation of America, a corporation of Delaware Application December 20, 1943, Serial No. 514,964

12 Claims.

particularly to a frequency modulation receiver of novel construction and performance. The generic expression angle modulated is intended to cover frequency modulation, phase modulation and hybrids thereof.

There has been disclosed and claimed by S. W. Seeley, in his application Serial No. 509,232, filed November 6, 1943, a control system wherein a double frequency modulated carrier wave is radiated to one or more separate receivers. Each receiver is capable of responding solely to a wave having a predetermined combination of carrier, sub-carrier and modulation frequencies selected at the transmitter. Reception is accomplished in a unique manner, and without radiation from a receiver unit. Each receiver unit, upon proper energization, is capable of operating a controlled device, as for example a land mine. In our ccpending patent application Serial No. 497,000, filed August 2, 1943, we have disclosed and claimed a particular transmitter unit adapted for utili- Zation in a system of the form shown in said Seeley application.

In our aforesaid copending application we have, in general, disclosed a transmitter unit wherein a selected carrier is frequency modulated (FM hereinafter for brevity) at a subcarrier frequency. The sub-carrier, in turn, is frequency modulated at a selected lower modulation frequency. The modulation current is pulsed at a repetition rate of approximately pulses per second by means of a telephone dial, which permits the transmission of from 1 to 10 audio frequency pulses per dial operation. At the completion of each dialed number the carrier is interrupted for an interval of approximately onetenth of a second. The secrecy of two million combinations is secured by using five carrier frequencies, five sub-carrier frequencies and eight modulation frequencies for a total of 200 combinations. At the receiver ratchet relays provide ten thousand combinations thereby providing a total of two million combinations.

At the receiver, as disclosed generally in the Seeley application, the complex multiple frequency modulated carrier wave is subjected to the discrimination action of highly selective tuned circuit-s. There is derived from the received FM wave an amplitude modulated carrier wave whose modulation frequency is the sub-carrier second harmonic. Detection of the derived energy yields an FM wave whose mean frequency is the said second harmonic and whose modulation frequency is the original modulation frequency applied at the transmitter. Further selective dis .crimination yields an amplitude modulated wave wherein'the modulation is the second harmonic of the original modulating frequency. After demodulation, the resulting second harmonic modulation is passed through a selective network, and employed to operate relays in a predetermined sequence.

One of the main objects of our present invention is to provide a receiver unit which is capable of satisfactory operation in a'system of the type shown by Seeley in his said application.

Another important object of our invention is to provide a reliable and efficientreceiver unit adapted to be responsive to any one of a selected frequency combination of thousands of possible combinations radiated from a transmitter of the type disclosed in our aforesaid copending patent application.

In the particular embodiment of .our receiver unit a novel detecting network and a novel relay arrangement are used. The received FM signal is amplified by a sharply tuned carrier amplifier resonant to the selected mean carrier frequency. Since the received signal is frequency modulated, the carrier may be thought of as varying in frequency above and below its quiescent frequency once each cycle of the modulating frequency. This process of modulation sweeps the carrier frequency back and forth across the singlepeaked resonance characteristic of the carrier amplifier thereby imparting'ampiitude modulation to the carrier. The resulting amplitude modulation has two maxima and two minima for each cycle of frequency modulation. Hence, the modulation frequencyis double, or the second harmonic of, the sub-carrier modulating frequency. Detection of the amplitude modulated carrier wave is followed by highly selective amplification in a so-called intermediate frequency network sharply tuned to the sub-carrier second harmonic frequency. As described previously, the result of this selective action is toprovide an amplitude modulated wave wherein the audio modulation frequency is double the original audio frequency.

Both the direct current and alternating current components of the following detector output cur: rent are used, Thedlrect current component is amplified, and is used to operate a sensitive relay which performs three functions. First, the filaments of an audio amplifier are turned on in the presence of the intermediate frequency (I. F.) current. Secondly, in the absence of carrier transmission for long intervals of time, the dialing and transfer ratchet relays are connected so that they automatically home. Thirdly, when carrier transmission is interrupted at the end of each dialed number the transfer ratchet relay is advanced one step.

The alternating current component of the detector is the second harmonic of the original audio modulation frequency. Thiscomponent is amplified in a tuned amplifier, rectified and utilized to operate a second sensitive relay. This sensitive relay controls the dialing ratchet relays of which there are four. Each dialing relay may be dialed to any one of ten positions. When the four dialing relays are in the correct position a circuit is completed, and the latter action connects a land mine detonator to a battery of the receiver power supply.

It may be stated that it is a more specific object of our present invention to provide a highly efficient and reliable receiver unit for use in a secrecy radio control system, wherein the receiver unit operates with no local oscillator or other radiating signal to derive the benefits of selecitivity and sensitivity of a superheterodyne circuit.

Still other features and objects of our invention will best be understood by reference to the following description, taken in connection with the .the drawings, in which we have indicated diagrammatically several circuit organizations whereby our invention may be carriedinto effeet.

In the drawings:

Fig. 1 schematically shows the networks of a transmitter unit adapted to control a receiver of the present invention,

Fig. 2 schematically'shows the networks of a receiver unit comprising the present invention,

Fig. 3 shows the circuit details of the receiver unit forming the subject matter of our present invention,

Fig. 4 shows the details of the relay circuits.

Before describing the circuit details of the receiving system shown in Fig. 3, the transmitter and receiver units will be generally described. In Fig. 1 we have depicted in purely schematic manner the generalnetworks employed in our aforementioned transmitter application Serial No. 497,000. The numeral l designates a source of modulation signals. Specifically, the network I is an audio frequency oscillator of the resistance-capacity (RC) type arranged with switching means to generate oscillations at a plurality of different selected frequencies. In a particular example eight frequencies falling between 200 and 1200 cycles per second are employed. The subcarrier oscillator 2 preferably generates oscillations in a range of 60 to 140 kc. A selector switch is provided in network 2 to permit the selection of any one of five sub-carrier frequencies. The selected. sub-carrier frequenc is deviated in accordance with a selected audio frequency. The FM modulator 3 is employed .to provide the frequency modulation of the selected sub-carrier oscillations. Preferably the amplitude of the audio oscillations is adjusted to a level to provide the correct amplitude todrive the modulator tubes in network 3. Each selection of a desired sub-carrier frequency .is, accordingly, accom- 4 panied by an appropriate selection of audio tone amplitude.

The numeral 4 denotes a manual dial through which during dialing operations the regulated output of audio source I is fed to the modulator tubes. The dialing mechanism is manually controlled, and pulses the audio frequency voltage at a repetition rate of approximately 10 pulses per second. This permits the transmission of from 1 to 10 pulses per dial operation, since the dial has 10 positions. The output of the dial t is fed to the modulator 3 to angle modulate the sub-carrier oscillations. In our aforesaid application we have shown the modulator as a pair of push-pull related reactance tubes to Whose respective control electrodes is fed in differential manner the output of dialing device 4. The reactance tubes of modulator 3 act to reduce concurrently the effective capacity reactance and inductive reactance of the tank circuit of oscillator 2, and Vice versa, thereby to change the frequency of the generated sub-carrier oscillations. The selected audio tone and amplitude causes the variation of the reactance tube effects.

The frequency modulated sub-carrier oscillations are now employed to modulate the carrier oscillations produced at network 5. The modulator 6, associated with carrier oscillator 5, is of the same construction as modulator 3. A pair of push-pull connected reactance tubes provide the modulation circuit for oscillator 5. The range of oscillator 5 is 5 to 10 mo, and any one of five carrier frequencies may be selected. Preferably, and as in the case of the sub-carrier frequency selection, we apply the modulated sub-carrier oscillations to modulator 6 in a balanced sense and of proper amplitude for constant deviation at the five different .carrier frequencies. In both the frequency modulation steps at oscillators 2 and 5 the frequency of the generated wave will be deviated to an extent dependent upon the amplitude of the modulating signal, while .the frequecy of the modulating signal determines the number of times per second that the change or deviation in frequency of the wave takes place. It is assumed that the amplitude of each of sources I, 2 and 5 is uniform, and that the waves are sinusoidal in character. These characteristics, however, are not restrictive. 1

After each dialing operation of dial device 4 the operation of carrier oscillator 5 is interrupted, for example, for approximately one-tenth of a second. This is done by employing for the control function a relay I which is energized for about one-tenth of a second after each dialing operation to render the oscillator 5 effectively inoperative. The numeral 8 denotes a control switch device for a relay 9, which when energized, acts to prevent the modulated output of oscillator 2 from reaching the modulator 6. Specifically, as shown in our aforesaid application, the switch 8 in tune position causes the relay 9 to be energized so that the grids of the reactance tubes of modulator 6 are grounded. When switch 8 is in operate position the relay 9 is in non-energized condition, and the connection from oscillator 2 to modulator 6 is normal. When the switch 8 is in tune position the frequency select-ion of oscillator 5 can readily be performed.

Remembering that the exciter output of oscillator 5 is one-quarter of the frequency at the carrier oscillations. Hence, there is passed on to remaining transmitter units wave energy having double frequency modulation and having a mean frequency in the 20 to 40 mo. band. The combinations of modulated excitation provide for 2,000,000 frequency combinations, or 400,000 combinations of any one selected carrier frequency. The secrecy of 2,000,000 combinations is obtained by using 5 carrier frequencies, 5 sub-carrier frequencies and 8 audio frequencies for a total of 200 combinations, which when multiplied by the 10,000 combinations provided by the ratchet rel-ays at each receiver unit gives a total of 2,000,000.

When a certain receiver is to be dialed the tuning dials of the oscillator I, oscillator 2 and carrier oscillator 5 are set, and the switch 8 is adjusted from tune t operate. The proper numbers are then dialed by the dial mechanism 4 for a receiver control operation, following which the relay 9 is returned to tune position if the next succeeding receiver control operation requires a different carrier frequency. In order to allow other'receiving equipment to home, that is permit their relays to return to their original settings, a period of 5 seconds should elapse before dialing another receiver having the same subcarrier and carrier frequencies. When one receiver is used to operate two or more detonators on different dialed numbers, this homing sequence must be carefully observed.

The receiving system of our present invention is schematically represented in Fig. 2. One or" the factors of prime importance in the receiving system, as disclosed and claimed in the aforesaid Seeley application, is that the receiver is so constructed that it will produce amplification at the second harmonic of a predetermined modulation frequency of an incoming carrier. The second harmonic is produced by the action of simple narrow-band tuned circuits at the carrier frequency. It will be remembered that in the usual receiver of FM carrier Waves the detector is customarily preceded by amplification of a broad band of frequencies at the carrier frequency followed by some type of discriminator. In the present receiver there is no discriminator network per se, since the discrimination is an inherent function of the sharp selectivity characteristic in each of the cascaded tuned circuits. The advantages of sensitivity and selectivity inherent in superheterodyne receivers are secured in this system, yet no local oscillator is employed with the result that no oscillatory energy is radiated from the receiver.

The received multiple frequency modulated carrier wave energy may be collected by any desired type of signal collector [4. Depending upon the installation of the receiver unit, the collector 14 could be a grounded antenna circuit, a dipole,

. or any other well known pick-up device capable of collecting wave energy whose mean carrier frequency is in the operating range of 20 to 40 me. The carrier amplifier [5 may be of any well known construction, and it has an input circuit which is sharply tuned to the selected carrier frequency of the received wave. The amplifier I5 is followed by a detector I8 whose tuned input circuit will be sharply tuned to the selected carrier frequency. It is desired that the resonance curves of the input circuits of amplifier l5 and detector l3 be of the same type.

Since it has been fully disclosed in the aforesaid Seeley application how the selective input circuit of the amplifier derives amplitude modulated energy from the double FM carrier, it is not believed necessary to repeat the description of the derivation in as great detail. It is sufficient for the purposes of Fig. 2 to point out that since the received modulated carrier wave is frequency modulated, the carrier may be thought of as varying in frequency above and below its quiescent frequency once each cycle of the modulating frequency. This process of modulation sweeps the carrier frequency back and forth across the singlepeaked resonance characteristic of the amplifier I5 thereby imparting amplitude modulation to the carrier. For each cycle of frequency modulation the resulting amplitude modulation has two maxima and two minima. Hence, there will be applied to the detector input circuit an amplitude modulated carrier wave whose mean frequency is the received carrier frequency, but whose modulation frequency is the secondharmonic of the sub-carrier frequency.

The detector 18 acts to rectify the amplitude modulated carrier wave energy. The detected energy is frequency modulated wave energy whose mean frequency is double the sub-carrier fre quency, and whose modulation is made up of a component provided originally by the audio frequency oscillator l of the transmitter unit. The frequency modulated wave energy of double the sub-carrier frequency is termed intermediate frequency energy (I. F. for brevity). The term should not be understood as implying the use of a local oscillator as is done in superheterodyne receiver practice. The expression I. F. is used herein, because the second harmonic sub-carrier frequency is intermediate the received carrier frequency and the original audio modulation frequency.

The I. F. energy output of detector I8 is amplified by an I. F. amplifier 2! whose input circuit is highly selective, and is tuned sharply to the second harmonic of the sub-carrier frequency. The sharp selectivity characteristic of the input circuit of amplifier 2| acts in the same manner as do the sharp input circuits of amplifier I5 and detector l8. In other words, the FM wave energy applied to the input circuit of I. F. amplifier 2| is translated into amplitude modulated wave energy whose mean frequency is the second harmonic of the sub-carrier frequency, but whose modulation frequency is double the original selected audio frequency. This means that there will be applied to the sharply tuned input circuit of the following detector 23 an amplitude modulated wave whose mean frequency is the I. F. value, but whose modulation frequency is the second harmonic of the selected audio frequency.

Both the alternating current and direct current components of the detected output current of detector 23 are utilized. The direct current component is amplified by the direct current amplifier 24, and the amplified output of amplifier 24 operates a sensitive relay 25 Which performs three functions. First, the filaments of an audio amplifier are connected in a complete heating circuit in the presence of I. F. energy. Secondly, in the absence of carrier transmission for long intervals of time, the dialing and transfer ratchet relays are connected so that they automatically home. Third, when the operation of the transmitter is interrupted, at the end of each dialed number, the transfer ratchet relay is advanced one step.

The alternating current component of the detected output of detector 23 is amplified by the audio frequency amplifier 26. It is preferable to have amplifier 26 tuned to the second harmonic of the selected audio frequency. The rectifier 21 rectifies the output of tuned audio amplifier 23. The output voltage of rectifier 21 operates a second sensitive relay 28. This relay 28 controls the dialing ratchet relays, of which there are four, located at 29. The detonator 30 is actuated in accordance with the operation of the relays located at 29.

It will now be seen that in general in the detecting system used at the receiver a form of double demodulation takes place, and at the I. F. amplifier 2| there is provided a doubling of the tone frequency. In other words, where the audio oscillator at the transmitter is adapted to operate at a selected one of eight frequencies running from 200 to 1200 cycles, at the output of detector 23 in Fig. 2 one may select a tone frequency from eight frequencies located in the range of 4.00 to 2400 cycles. The detected output of detector 23 includes, in addition to the selected double frequency tone, a direct current component which is derived from the rectified carrier. The selected tone frequencyis used to step up one of a series of dialing sensitive digital relays, there being four in this embodiment. More may be employed, if desired. Absence of the direct current component is used to transfer operation 'of the tone frequency from one digital relay to the next.

Since in the operation at the receiver it is desired to interrupt the direct current component thereby to operate the relay 25, the rela 1 is provided at the transmitter unit in Fig. 1 for interrupting the carrier oscillator operation after each dialing operation. As stated previously, at the transmitter unit the audio frequency is pulsed by the dialing mechanism 4 at a repetition rate of about ten pulses per second, this permitting the transmission of one to ten audio pulses per dial operation. At the completion of each dialed umber t Operation of the carrier oscillator is interrupted approximately for one-tenth of a second. This interruption is used to operate the transfer switch at the receiver unit which conditions a second digital ratchet relay for operation, assuming that the first one was operated by the dialing described above. The digital relays, and other relays, at the receiver unit are frequency sensitive, and respond to one particular tone frequency only. When the four digital relays are in the correct position, which has been predetermined, a circuit is completed which consistor42 and lead 43.

nects the land mine detonator, or any controlled I circuit, toan energizing source.

Attention is now directed to the detailed circuit diagram of Fig. 3 wherein is shown the specific circuit connections of one embodiment of 'a receiver unit. The carrier amplifier network l5 consists of a pair of cascaded tuned amplifier stages. Of course, more than two stages of carrier-tuned amplification may be employed. The first tube 3| and second tube 32 are illustratively represented as pentodes, although any other suitable type of tube may be used. The signal grid 33 of tube 3| is connected to one end Of a tuner coil 34 which is of the adjustable iron core type. The lower end of coil 34 is connected to ground through condenser 35. The direct current return path for grid 33 consists of the choke coil 36. Energizing current sources 31 and 38, both shown as battery sources by way of illustration, are provided for the screen, plate and cathode electrodes.

The plate electrode 39 of tube 13| is connected to the positive terminal of direct current source .31 overa path comprising choke coil. 43 and; lead 4|. The screen electrode is connected to an appropriate positive Voltage point on battery 31 over a path consisting of voltage reducing re- The grounded suppressor grid and the positive screen electrode are appropriately bypassed to ground for high frequency currents. The filament 44 of tube 3| is connected across the heating current source 38 by virtue of its connection between ground and lead 45.

The coil 34, condenser 35 and the input capacitance of tube 3| (designated by the dotted condenser 46 between grid 33 and the grounded cathode or filament 44) provide a resonant input network for amplifier tube 3|. The input network 34-3546 is tuned to the desired carrier frequency of the collected double frequency modulated Wave energy. The inductance of coil 34 may be chosen so as fixedly to tune the amplifier to any of the following five carrier frequencies: 21, 25.5, 30, 34.5 and 39 me. These are, of course, purely illustrative values. These values will correspond to the carrier frequencies selectively radiated from the transmitter, it being understood that in the present example of our invention the radiated frequencies are four times those produced by the carrier oscillator 5 of Fig. l.

The antenna input transmission line 47 may be connected to feed across condenser 35. The line 4? is preferably designed to operate out of a quarter wavelength antenna normally having a resistive output impedance of 35 ohms. The coupling between line 31 and the input network of the tube 3| is below critical to the extent that a reactive component in the antenna impedance equal to the antenna resistance does not detune the input network. Hence, the antenna connected to line 47 could vary considerably from a quarter wavelength without detuning the input network 3435-45. The resonance curve of the latter network is sharply peaked by virtue of proper selection of the Q of coil 34.

The second carrier amplifier tube 32 has its electrodes energized in the same manner as tube 3|. The filament of tube 32 is connected to the heating source 38. The screen and plate are connected to leads 43 and 4| respectively. The choke coil 43 is in circuit with the plate and lead 4|. The control grid 48 of amplifier tube 32 is connected by direct current blocking condenser 49 to the plate end of coil 40. The coil 34 is an iron core tuner coil, similar to coil 34, and acts to tune the input circuit of tube 32 to the desired carrier frequency. The coil 34' also functions as a direct current return path for grid 48.

The iron core of coil 34 is adjusted so that the selected inductance thereof will resonate with the output capacitance of tube 3| and the input capacitance of tube 32 to the received carrier frequency. The output and input capacitances are shown in dotted lines, and are designated by reference numerals 50 and 5! respectively. The

tuned network 34'53-5| has a high Q; its

resonance curve has a sharp peak at the selected carrier frequency. The plate circuit of amplifier tube 32 is impedance-coupled to the diode section of multiple functiontube 52. The latter may be a diode-pentode tube, or it can be'any other type of tube or two separate tubes providing a diode section and an amplifier section.

The filament 53 of tube 52 is heated from source 33. The diode anode 53 receives its electrons from a portion of the filament surface. Anode 53 is connected to the grounded leg of the filament through a series path consisting of coils .54 and 55.. Bothcoils preferably have adjustable iron cores. The junction point '55 of the coils 54 and 55 is connected to the control grid 56 of the amplifier section of tube '52. Condenser 51 shunts coil 54, and tunes the latter to the second harmonic frequency of the sub-carrier frequency employed at the transmitter. Coil 55 and the inherent diode capacitance 58 provide a resonant input network for diode 53-53 sharply tuned to the carrier frequency. The capacitance 58 is shown dotted, since it is the inherent anode to filament capacity of the diode. The tuned circuit 54-51 acts as the diode load. At the same time it is the tuned input network of the amplifier section of tube 52. The anode 53 is connected by direct current blocking condenser 59 to the plate end of choke coil 45'.

The cascaded amplifiers up to the diode 53-53 act'to provide simultaneous discrimination and amplification of the received double frequency modulated carrier wave. The efiect of the cascaded sharply tuned circuits 34-35-45, 34'-5l and 55-58'is to translate substantially all the frequency modulated carrier wave energy into amplitude modulated carrier energy whose frequency of modulation is of double the sub-carrier frequency. The specific manner in which each of the cascaded highly selective circuits acts to provide such discrimination has been fully explained in the aforementioned Seeley application. Frequency modulated wave energy whose mean I frequency is of double the sub-carrier frequency is derived by detection in the tuned diode circuit. The output voltage developed across tuned load 54-51 is the so-called I. F. voltage, which is shown in Fig. 2 as amplified at 2 i.

The I. F. energy developed at tuned diode load circuit 54-51 is amplified in the cascaded I. F. amplifier tubes 52 and 58.. The screen grid and plate of tube 52 are connected to lead 4| through separate voltage reducing resistors SI and BI of equal Value. The shunt feed coil 40" is in series with resistor El, and the junction of the two elements is bypassed to ground for carrier currents by condenser 62. A parallel resonant circuit, consisting of coil 65 and condenser 55, functions as the sharply tuned input circuit of tube 60. The plate of tube 52 is coupled through direct current blocking condenser 63 to the high alternating potential side of tuned circuit 65-55 and to the control grid 64 of I. F. amplifier tube 50.

The tuned circuit 65-55 resonates at the I. F. and has a high Q so as to provide a sharply peaked resonance curve as in the case of tuned I. F. circuit 54-51. Similarly to the prior amplifier tube, the tube 50 has its screen grid connected through a properly bypassed voltage reducing resistor to lead 43. The plate of tube 50 is coupled to the control grid 58 of multiple function tube 69 by means of a pair of reactively coupled tuned circuits, each tuned to the I. F.: The tuned circuit connected with plate 51 consists of iron core coil 10 shunted by condenser 1|. The second tuned circuit consists of iron core coil 12 shunted by condenser 13. Coils 1i) and 12 are magnetically. coupled to provide a resonance curve sharply peaked at the operating I.'F. value (second harmonic oftransmitter sub-carrier frequency) The lower end of coil 10 'isiconnected through bypassed resistor 14 to supply lead The lower end ofcoil 12 is returned to ground, and the filament of tube 55 is heated by sou1'ce'38. As in the icase of tube 52, the screen and'plate of .the amplifier section of tube .65 are connected through bypassed voltage reducing resistors 15 and 16 to supply lead 4 l The pentode section of tube 59 functions as an amplitude limiter. The resistors 15 and 16 are chosen in magnitude so that the pentode section of tube 55 readily saturates in response to excessive amplitude of signal voltage at grid 68.

In the plate circuit of the amplitude limiter section there is included a parallel resonant circuit 11-18 similar in construction to tuned circuit 'll-ld. The coil 18 is magnetically coupled to coil 19 of parallel resonant circuit 19-80, connected between diode anode 8i and the upper end of diodeload resistor 82. The lower end of resistor 82 is connected to the grounded leg of the filament 81' of tube 59. It will be understood that circuit 19-80 is the tuned input circuit of diode 8 l-BI', and is connected in series with the unbypassed load resistor 82. Magnetic coupling between coils l8 and 19 is chosen so as to provide sharp selectivity for the diode input circuit. The resonance curve of coupled circuits 11-18, 19- 88 will have a sharp peak at the I. F. Value.

It will be appreciated that detector diode 81-8! is preceded by a plurality of cascaded highly selective resonant networks 54-51, 65-65, 11-10-12-13 and 11-18-19-80. In each of these networks frequency modulated I. F. energy is converted into amplitude modulated I. F. energy whose audio modulation is double the selected audio modulation selected at network l of the transmitter unit (see Fig. 1). Thus, there will be a maximum of FM energy converted due to the large number of sharply tuned circuits preceding the detector. There will occur concurrent amplification of converted I. F. energy at tubes 52 and 50. However, at tube 59 amplitude limiting is accomplished so as to control the level of the audio output of detector 23, and hold it within usable limits. The plate circuit limiter 59 permits a variation of audio output of approximately 3:1. The I. F. amplifier should be sufiiciently sensitive so as to provide an output at the detector 23 which is sufficient to operate the following networks 24, 26 and 21.

The diode 81-31 detects the limited modulated I. F. energy applied thereto from circuit 19-85. There will be developed across load resistor 82 a direct current voltage component and an audio frequency voltage component. The audio voltage component 'has a frequency which is double the original modulation frequency. The audiovoltage and the direct current voltage are both applied over a common lead 83 to an audio amplifier 26 and a direct current amplifier 24 respectively. The'lead 83 is designated as the dialing and transfer path since the direct current component controls the transfer relay, Whilethe audio component controls the dialing relay. Both of these relays will be described in more detail in connection with Fig. 4.

Considering first the direct current amplifier 24, it consists of a tube 84 which is directly coupled to a following tube 85. The filaments 84' and 85' of'tubes 8d and 85 respectively are heated by the heating current source 38, and the ungrounded leads of these two filaments are connected by a common lead 85 to the heating supply lead 15. The control grid 81 of tube 84 is connected by a resistor 88 to the common'lead 83. It will, therefore, be seen that grid 81 returns to ground through'a path consisting of resistor 88, lead 83 anddiode load resistor 82. The screen grid of tube 84 derives its positive voltage from lead 43, while the plate 89 isconnected by means llof the plate resistor 9H and lead 99 to the positive voltage supply lead 4i. The plate end of'resistor- 95 is connected to ground by condenser 51% in order to bypass the audio component.

Tube 85 has its control grid 92 directly connected to the plate 89 through a negative biasing battery 533. This battery shouldbe wellinsulated from the chassis, and preferably applies a negative bias of about 45 volts to grid 92. The screen grid 54 and the plate 95 of tube 85 are connected in common to the positive voltage supply lead 4|. This connection is made over a path comprising lead 96, transfer relay winding 9-7 (Fig. 4), lead 98, lead $9 andlead 4I. Condenser I I39 shunts the winding 91.

In order to explain the operation of tubes 84 and 85, let it first be assumed that no carrier is being radiated from the transmitter unit shown in Fig. 1. This will happen, for example, when after a number is dialed the carrier oscillator is momentarily rendered ineffective. In this nocarrier state the tube 84 is conductive, and provides a voltage drop across the plate load resistor 96. This causes a reduction in the plate potential to a small positive value. This small positive voltage at the plate end of resistor 90 is not enough to prevent the high negative bias of battery 93 from cutting off the plate current fiow of tube 85. Hence, there will be no current flow through the winding 91 in the absence of received carrier energy.

On the other hand, when carrier energy is being received, the direct current voltage developed across resistor 82 will be applied to the grid 8! in a negative polarity. This negative voltage applied to grid 81 considerably reduces the flow of plate current through resistor 90 with the result that the voltage drop across the resistor decreases. Hence, the plate potential of tube 84 effectively rises in a positive sense until it offsets the cut-off bias due to battery 93 to an extent such that current flows through the plate circult of tube 85 and through the transfer relay winding 91.

The unit 24 is actuated by the momentary suppression of the carrier to elfect transfer operations from one dialing relay to the next dialing relay. It will be noted that tube 84 operates at zero grid potential. Normally, and merely by way of illustration, the plate 89 could be allowed to be positive by only +20 volts in the absence of received carrier energy. This Would provide a net'bias for grid 92 of about 25 volts, which is double the negative voltage necessary to cut off' the plate current of tube 85. If now carrier energy is received, and say for example one volt of negative voltage is applied to grid 81, th plate 89 would have a potential of about +82 volts. This would permit the application of +37 volts to grid Q2 thereby permitting maximum plate currentto fiow through the sensitive transfer relay winding 91. Such maximum plate current would be some five times the current necessary to close the transfer relay.

' To prevent the audio component, which is also applied to grid 87. from biasing the output tube, and also to prevent relay clicks and spark discharges from operating this relay, considerable time-delay and bypassing is provided by condenser i and the shunt condenser I 00. The total time dela produced by these two bypass condensers. must be less than thetime intervals between dialingthe numbers 11-11 as rapidly as will ever be required; This is another way of saying that the delay must be short enough of our invention will operate its associated-relay 9? when the input voltage on. grid 8'! is more" negative than 0.6 volt (D. C.) which will occur for the minimum operable signal on the receiver.

Moreover, the. sensitivity of the am-- antenna. pifier is not appreciably impaired toward the end of the life of the plate voltage supply source 31, because of the initial excess during reception of operable signals of positive grid potential onthe grid 92 of tube 85. 1

Considering now the utilization of the audiocomponent provided across load resistor 82; the audio voltage is supplied throug-hthe direct current blocking condenser IflI to the control grid I: of tube Hi3. The tube Q93 function along with the following tube M14 as a selective audio frequency amplifier. The final tube IIl5 functions as a plate rectification type of detector. The filaments I03, I04 and I05 of the three tubes have one common lead I06 to the positive terminal of the heating current source II", the negative terminal of source IO'I being grounded. The remaining filament lead of each of tubes 93, 484 and IE5 is connected to a common lead i iil. The lead I08 returns to ground through a path (see Fig. 4) consisting of lead I09, contact point Hi), contactor III, armature I42, lead ,l39 and lead I40. It will, therefore, be seen-that the filaments I03, I04 and I05 will not be heated unless the switch I IIlI I I is closed.

In the plate circuit of each of tubes I03 and lll l there is provided a parallel resonant circuit which is tuned to the second harmonic of the audio frequency selected at the network I of the transmitter unit in Fig. 1. The plate II3 of tube 03 is connected to the high alternating potential side of the first resonant circuit. The latter consists of a coil I I4 shunted by condenser H5. The

low potential end of coil H4 is connectedto a lead IIB, which, in turn, is connected to the positive terminal of the plate voltage supply source 37. A damping resistor H1 is connected in shunt with the parallel resonant II4I'I5, and the screen grid of tube N13 is connected to the lower end of coil H4. The control grid I02 i returned to ground through a resistor I02, but the control grid I.I8 of tube I 04 has a negative bias of about -9 volts applied thereto from a negative biasing source H9. The direct current blocking condenser IZE couples grid H8 to the upper end of coil II4, and the biasing lead IZI includes the grid resistor I22 in circuit therewith.

The plate circuit of tube I64 similarly includes a parallel resonant circuit consisting of coil 4': shunted by condenser H5. The damping resistor. H1 is connected in shunt across the sec ond resonant circuit, and the plate and screen grid of tube I04 are connected to the upper and lower ends of coil lM' respectively. The lower end. of coil H4" is connected to the voltage'supply lead II6. trol grid I23 connected through the grid resistor 12.4 and lead I25 to the negative terminal of the biasing source H9, and a negative bias of about -l6 volts is normally applied to grid I23. The

plate I26 of tube I05 is connected to the positive The; amplifier- The detector tube I05 has its con- The unit 26-21 provides audio selectivity, and utilzes the audio dialing pulses to operate the dialing relay I28. Assuming by way of illustration that at the transmitter the selected audio frequency was 430 cycles; then each resonant circuit II4I I5 and II4'I I5 would be tuned to 860 cycles. The 860 cycle voltage developed across the second tuned circuit is sufiicient to exceed the l6 /2 volt normal bias on the grid I23 of the plate circuit detector tube I05. This detector tube has sufficient current capacity so that no direct current voltage amplifier is required subsequent to rectification. The increase in grid voltage from beyond cut-off increases the plate current flow of tube I05 through the winding I28 from zero to approximately twice the current required to operate the relay. The large bypass condenser I30 across the detector plate circuit provides time delay and also integrates the half waves of audio frequency that would otherwise appear across this circuit. The delay and integration is desirable short of the failure point of the fastest dialing operation which will ever be required. Such failure might result from too long a holdover for the sensitive dialing relay, precluding its release.and recovery within the time between two dialing pulses. Short of this point, the delay and integration is desirable in that it makes the dialing operation relatively immune to interference resulting from relay clicks and other extraneous pulses from the transmitter, or from external sources such as ignition interference, unless it is strong and of long persistence.

Each of the tuned audio circuits is shunted with a resistor. The first tuned audio circuit II 4--I I5 is shunted by a resistor III, while the second tuned audio circuit I I4 I I5 is shunted by a resistor H1. The function of these resistors is to prevent shock excitation of the tuned circuits. The damping of these circuits is a cornpromise between immunity from shock excitation and necessary selectivity. The resulting selectivity is sufficient to preclude operation by adjacent audio frequencies. As stated above, the filaments of the tubes of the dialing unit 26-2'I are closed upon closure of switch IIll-I I I. This switch is closed only when the homing relay is actuated to disconnect the homing circuits. That is, the audio amplifier heaters are not connected in circuit with source Ifl'I until current flows through the transfer relay winding 91. This has the desirable features of diminishlllg the drain on both the plate and filament supply batteries, except preparatory to dialing.

Reference is now made to Fig. 4 for a detailed explanation of the manner in which the various relay functions are performed. It is to be understood that the circuit shown in Fig. 4 is a continuation of the circuit shown in Fig. 3 to the right of the vertical dotted line A-A. Upon flow of current through winding 9! of the transfer relay the armature I3i. is pulled towards the position in which fixed contact I3I and movable contact I32 touch. This breaks the connection through movable contact I32 and fixed contact I33. Upon closing of switch I32-I3I the winding I34 of the homing relay is placed in an electrical circuit with the relay battery I35 which has a potential relative to its. grounded negative terminal. of about +90 volts. The resulting electrical circuit through the homing relay may be traced over the following path: from the positive terminal of battery I35 by lead I35 to common relay lead I31, thence to armature I34 and switch I32I3I to lead I38, through winding I34 to lead I39, and

through lead I40 to the grounded negative terminal of battery I35.

A condenser I4I bypasses the switch I33-I32 when the latter is closed. Condenser I4I shunts the homing relay winding I34 to provide a time delay of 2.0 seconds. Upon closing of the aforesaid electrical circuit through winding I34, the latter is energized and the armature I42 is pulled towards the electromagnet. This causes closing of switch IIIl--I I I. Armature I42 has associated therewith a second movable contact l43. Contacts III and I43 are spaced from each other by the insulation spacer I44, but are nevertheless connected in common by lead I39. The contact I43 cooperates with a pair of fixed contacts I45 and I45. Normally the switch consisting of contacts I43 and I46 is closed, while switch I45I43 is open. Upon closure of switch III]--I I I, as pointed out previously, the filaments of audio tubes I53, I44 and I are connected in circuit with heating source It". The tubes become operative to energize the dialing relay winding I28.

Upon energization of winding I28, the armature I4! is attracted thereby closing the switch consisting of movable contact I48 and fixed contact I49. The armature I 4! is connected at its pivoted end to ground by lead I50. The fixed contact I49 is connected to lead I5I by resistor I52. Condenser I53 connects the right hand end of resistor I52 to ground. The lead I5I is connected to predetermined ones of a circle of spaced contacts I54. A second circle of spaced contacts 555 is provided concentrically with the contacts I 54. Corresponding contacts I54 and I55 are aligned radially so that a rotatable metallic connector I56 may electrically connect them in pairs. This connector may be of any desired shape; preferably it should be a metal plate whose inner end is secured to an insulation carrier bar I51.

The connector unit I5I-I53 is mechanically mounted for rotation about an axis or shalt assumed to be passing through the common center of the circles of contacts I54 and I55. Rotation of the contactor unit in a clockwise direction will then be seen to provide sequential electrical connection between the respective pairs of contacts I54 and I55. The connector unit is rotated in a clockwise direction by means of a pawl and ratchet designated by numerals I58 and I59 respectively. The dotted line I60 schematically represents a common mechanical coupling, such as a shaft, upon which is mounted the ratchet I59, the connector unit ISL-I55 and cam ISI. The cam IGI generally has the shape of a disc, except that it is provided with a recess I52. The mechanical structure of the ratchet I59, cam IBI, connector unit I5l'-I53 and shaft I54 are schematically represented, but it is to be understood that those skilled in the art are fully aware of the manner of constructing these units. It is sufiicient for the purposes of this application to point out that upon rotation of the ratchet I53 the cam IBI will concurrently be rotated, as will also the connector unit I5'I-I55. It will, also be understood that when the ratchet I59 is rotated through an angular distance equal to one tooth, the connector I53 will be moved from one pair of aligned contacts to the immediately following pair of contacts in a clockwise sense.

The pawl I58 is pivotally secured to the armature I63 of a digital stepping relay.- The numeral I64 denotes the winding of the electromagnet of that relay. This relay is the transfer step relay of a bank of five stepping relays. Condenser I65 shunts the winding I54, and the upper end of the pivoted spring follower of cam I6I.

15 the winding I64 i connected by lead I66 to the contact point I33. The lower end of winding I64 hasone connection I61 to the fixed contact point I45, while a second connection I68 is connected to the fixed contact point I69. The mobile contact I10 is electrically associated with contact point I 69, and the former is carried by the armature I63.

Hence, it will be seen that when winding I64 is unenergized, the armature I 63 will be in its released position and switch I10I69 will be closed, Of course, the pawl I58 will be in its lowermost position. The pivoted end of armature I63is connected to'a fixed contact point I'll which ha a spaced mate contact I12. Contact points HI and I12 have electrically associated therewith a mobile contact I13, which actually is The follower I13 is provided with a convex portion I14 adjacent its free end. This portion I14 rides along the cam periphery of disc I6I and is normally seated in the recess I62.

. The pivoted end of cam follower I13 is electrically connected to the fixed contact point I46. Accordingly, when the homing relay winding I34 is energized to attract its armature I42, the switch I43I46 will be opened, while switch I45- I43 will be closed. Furthermore, switch I1II13 will be closed, as shown in Fig. 4, during the time that the cam follower rides out of recess I62 and along the cam periphery. It follows, therefore, that when the convex portion I14 is seated in recess I62, switch I13I1l will be opened, while switch FIB-I12 is closed.

Each of the remaining members of the group of digital relays is constructed in the same manner as described in connection with the first stepping relay. Thus, the second stepping relay has a winding I whose upper end is connected by lead I16 to the common conductor I31. The lower end of winding I15 is connected by lead I11 to one'contact of the circle of contacts I55. This one contact is designated by numeral I18, and it will be noted that the contact I18 and its mate I18 are in the twelve oclock position of the connector unit. The lower end of winding I15 is, also, connected to the fixed contact point I19. The armature associated with winding I15 is designated by numeral I86. The pawl IBI is pivotally carried by armature I80, and ratchet I82 is provided adjacent the free end of pawl NH. The common mechanical coupling for ratchet I82 and cam disc I84 is denoted by dotted line I63. The concentric circles of contacts are designated by numerals I65 and I 86. The mechanical driving means I63 is provided with the connector unit consisting of the insulation carrier bar I81 and the metallic connector plate I88. The cam follower I 89 for the cam disc I84 has its pivoted end connected by lead I90 to the fixed contact point I12. The cam disc is provided with recess I9I, and the cam follower has associated therewith the pair of fixed contacts I92 and I33. The fixed contact I92 is connected to the armature I80, while the fixed contact I93 is connected by lead I94 to the cam follower I95 of the third stepping relay unit. As in the case of winding I64, the

winding I15 is bypassed by condenser I15.

In the following stepping relay unit the relay winding I96, bypassed by condenser I96, is provided with an armature I91. The pawl I98 is pivotally secured to armature I91, and the free end of the armature functions as a mobile contact I99 for the fixed contact point 200. The lower end of winding I 96 is connected'bylead 2III to the second contact 202 of the circle of contacts I55. The upper end of winding 196 is connected by lead I66" to the common conductor I31, while lead 281 is electrically connected to the fixed contact 266. The common mechanical coupling 263 is provided with the ratchet 204, a cam disc 205 and the connector unit. The latter consists of the insulation bar 206 provided with the metallic connector plate 201. The outer circle of contacts for this connector unit is designated by numeral 208, while the inner circle of contacts is designated by numeral 269. The cam follower I is associatedwith the spaced fixed contacts 2H] and 2H, while the cam disc 205 is provided with the recess 2I2.

The penultimate step-ping relay unit comprises winding 2 I 3 whose upper end is connected by lead 2I4 to the common conductor I31. Bypass condenser 2I3 shunts winding 2I3. The lower end of Winding 2I3 is connected by lead 2I5 to contact 2 I 6 following contact 202 in a clockwise sense. The common means 2I1 mechanically couples ratchet 258, cam disc 2I6 and connector unit 220-221. The outer circle of contacts is denoted by numeral 222, while the inner circle of contacts is designated by numeral 223. The armature 224 has its pivoted end connected to fixed contact 225; the opposite fixed contact is 226. The cam follower 221 has its pivoted end connected by lead 223 tothe fixed contact 2i I. The recess 229 is provided in the cam periphery ofdisc 2 l 9. Armature 224 is provided with pawl 230 and mobile contact 23L The fixed'contact 232is connected to the lower end of winding 2 I 3.

The final relay unit comprises the winding 233, bypassed by condenser 233, whose upper end is connected by lead 234 to conductor I31. The lower end of winding 233 is connected by lead 235 to the outer contact 236 following contact 2I6 of the circular row of contacts I55. The fixed contact 231 is, also, connected to the lower end of winding 233, Common means 238 mechanically couples ratchet 239, cam disc 240 and connector unit 242-243. Recess 24I is provided in the periphery of disc 246. The connector-unit cooperates with the concentric circles of spaced contacts 244 and 245. The cam disc 240 has associated therewith cam follower 246, and only one fixed contact 248 is provided here. The lead 241 connects the pivoted end of follower 246 to the fixed contact 226. Armature 249 of the relay has the pivoted end thereof connected to contact 248. The armature is, furthermore, provided with pawl 256 and mobile contact 25 I.

In order properly to understand the functioning of the various relay units it is necessary to appreciate that the ultimate circuit through the controlled device can be closed only when the connectors I56, I68, 201, 221i and 243 are in electrical contact with respective predetermined pairs of contacts. In Fig. 4 there is shown the finally adjusted positions of the connector units to close the controlled circuit. The closed circuit is traced as follows: from the positive terminal of battery I35 to lead I36, then through lead 252 to inner contact 245', then through connector 2513 to outer contact 244 connected to lead 253, then through inner contact 223', plate 272i and outer contact 222 to lead-254, then through inner contact 269', plate 261 and outer contact 268' to lead 255, then through outer contact I, p1ate I68 and inner contact I86' to lead 256, then to lead 251'through outer contact I55, plate I56 and inner contact .I 54', and then through the controlled device back to the grounded negative terminal of battery I35.

It will be seen that unless the connector plates are adjusted to their respective pairs of contacts, as shown in Fig. 4, the controlled circuit will be broken. The function of the stepping relays is selectively to adjust in a sequential manner the various connector units. The order of adjustment chosen for illustration in this application is the case Where connector plate I88 is at the 5 oclock position; plate 201 is at the 7 oclock position; plates 22! and 243 are at the 9 oclock positions; and plate I56 is at the 4 oclock position. The adjustment of plate I56 to its ultimate position takes place after the dialing of 5'799 at the transmitter for control of the relays having windings I15, I93, 2I3 and 233 respectively.

In order to explain the operation of the entire system, let it be assumed that no carrier is being radiated from the transmitter. In that case (Fig. 3) there will be no direct current voltage developed across resistor 82, and tube 84 will have no effect on the normally inoperative detector tube 85. Hence, no current will flow through transfer relay winding 97. Consequently switch I3 II32 will be open thereby causing the homing relay to be de-energized. As a result switch I I--I II will be open thereby breaking the filament heating circuit of the audio tubes I03 and I04 and rectifier tube I95. Let it, also, be assumed that ratchets I59, I82, 204, 2I8, 239 are in normal positions. units are at 12 oclock positions on their respective concentric circles of contacts. Also, cam followers I73, I89, I95, 221 and 246 have their respective convex portions seated in their respective cam recesses I62, I9I, 2I2, 229 and 2M. Consequently switches ITS-I12, I89-I93, I952II and 22I226 are closed.

Let us now assume that at the transmitter unit it is desired to dial the combination 5799 so that the controlled circuit will be closed at a particular receiver of the many thousands of receivers which have been located at predetermined points in a given area. The particular receiver will, of course, have been wired for control by such dialing combination. It is additionally assumed that there has been selected for the particular receiver in question a combination of frequencies as follows: audio modulation frequency.

then it will be necessary to adjust the frequency selecting devices of the networks to select the new combination of frequencies.

Of course, in the case of the selection of a new carrier frequency switch 8 (Fig. 1) should be thrown to the tune position, thus effectively preventing the modulated sub-carrier oscillations from being applied to the modulator 6. This may be taken as the standby condition of the transmitter. In this position of switch 8 the selector of carrier oscillator 5 may be adjusted to the desired frequency. Generally speaking, when a certain receiver is to be dialed, the audio and subcarrier selectors are set, and the transmitter is switched to operate. The proper numbers are then dialed by the dialing device 4 for a receiver control operation, after which the transmitter is again returned to its standby condition. This means that the transmitter has been conditioned to radiate the carrier only Without modulation. In order to allow other receivin equipment to home, a period of five seconds is allowed to This means that all connector elapse before dialing another receiver having the same sub-carrier. and carrier frequency values. When one receiver is used to operate two or more detonators on definite dialed numbers, this homingsequence must be carefully observed. To provide the maximum secrecy of operation the transmitter should radiate only during the initial carrier tune; that is, without sub-carrier modulation and duringactual dialing operations.

The transmitter now being assumed conditioned for the predetermined audio sub-carrier and carrier frequencies, the dialing mechanism 4 is actuated for-the numeral 5. Before explaining what takes place at the receiver when the numeral 5 is dialed, it should be understood that the radiation of the double frequency modulated carrier wave conditions the receiver in the following manner. Referring to Fig. 3 the input circuits of tubes 3I and 32 act to convert the frequency modulated carrier wave energy into amplitude modulated carrier wave energy of the same carrier frequency as is radiated from the transmitter, which would be 20 mo. due to frequency multiplication at network I0 of Fig. 1, and whose modulation is the second harmonic of the sub-carrier frequency. Simultaneously, this amplitude modulated carrier wave energy is amplified bytubes 3| and 32. Detection occurs by virtue of diode 53-53, and across the resonant load circuit of the diode there appears frequency modulated wave energy whose mean frequency is the second harmonic of the subcarrier frequency. In other words this is the socalled I. F. energy to be amplified by the I. F. amplifier 2| shown in Fig. 2.

The amplifier section of tube 52 and tube 60 provide amplification of the I. F. energy. In the resonant circuits up to diode 8 I-8 I there occurs conversion of the frequency modulated I. F. energy'into amplitude modulated I. F. energy, whose modulation is the second harmonic of the original 200 cycle audio modulation frequency. Tube 39 limits the amplitude of the energy fed to the diode 8I-,-8I. The direct current voltage component of the rectified voltage developed across resistor 82 is applied over lead 83 to the grid 81 of tube 84,. This causes less current to flow through the plate circuit of the tube and thereby permits the plate end of resistor 90 to assume an increased positive potential. This potential is sufliciently positive to overcome the normal cut-off bias due to battery 93. As a result tube becomes conductive and permits current to flow through the transfer relay winding 91.

As a consequence of the energization of winding 91 the armature I30 is attracted and switch I32I3I is closed. It must be remembered that the application of the audio voltage component developed across resistor 82 to the grid I02 of audio amplifier I03 results in amplification of the 400 cycle voltage, this amplification being repeated by tube I04. The rectifier tube I05 provides current for the dialing relay winding I28. The tubes I03, I04 and I05 are capable offunctioning, because as soon as the switch I32I3I closed, the electrical circuit through the winding I34 of the homing relay was closed as heretofore explained in this application. Energization of the homing relay caused attraction of the armature I42 with the result that both switches 0-- III and MES-I43 were closed. Closure of switch IIIl-I II completed the electrical circuit including th filaments I03, I04 and I05 and the heating current source I01, as has been previously described.

Returning now to the explanation of what happens as the numeral is dialed at the transm'itter, there will be five pulses of current flowing through the dialing relay winding I28 at the receiver. This results in a similar actuation of the armature I l'I with the result that switch Mil-I49 will be closed five times. Since it has been assumed that the connector plate I56 is at its twelve oclock position, this means that plate I56 electrically connects the contacts I18 and 11-8. Hence, there will be established the following electrical circuit during the dialing of the numeral 5; from switch I 48l 49' through resist'or I52 and lead I5I to lead I'I'I through contact H8, connector plate I56 and contact I18, then through the relay winding I15 and lead I16 to common conductor I31, then through lead I36 and battery 135 back to the grounded side of sWitchIdB-MQ.

' As a result'of the aforementioned circuit being closed the relay winding I15 will have five pulses of current flow therethrough, and will thereby step the ratchet I82, by virtue of the action of armature 18c and pawl I81, five times in a clockwise direction. This will cause the connector plate 538 to be "adjusted to the five o'clock positionshown in Fig. 4. At the same time that this adjustment is happening the 'cam disc I84 has been rotated in the clockwisedirection. As a result the cam follower rides out of recess I9I and rides along the periphery of the cam disc to substantially the position shown in Fig. 4. Consequently the switch i93I89 'is opened, while switch I92 I'89 is closed.

It was previously pointed out that the relay 1 at'the transmitter unit (Fig. 1) is actuated at the end of each dialing operation. The function of relay 7 is momentarily to interrupt carrier radiation so as to permit the transfer function to t'ake'place at the receiver. The relay 1 in Fig. 1 is so connected that it is energized for 6 of a second'afte'r'each dialingoperation. This relay, as fully disclosed in our aforementioned application, interrupts the production of carrier oscillations. Upon this momentary interruption of the carrier the direct current voltage component'a'cross resistor 82 of Fig. 3 vanishes. Consequently, the current flow in tube 8'4 will increase to a point such that the positive voltage at "the Dlatefend of resistor '90 is insufiicient to prevent "biasing source '93 from cutting off tube 85. 'This results in the transfer relay releasing armature 13%? thereby opening switch 'I3I--I32 and closing switch l32-I33. The homing relay willnot release by virtue of the fact that it has atiine delay of two seconds. If the transfer relay were released longer than the holding time of the homing relay (as would happen if the transmitter were shut off), the homing relay would delay about two seconds due to the charge leaking off the condenser I'dI'across this relay and then release with results which are further set forth below.

'Si'rice'releaseo'f armature I36 has closed switch I33-I32, and since switch l45i43 is closed due to the energization of the homing relay, thre is completed an electrical circuit through therel'ay winding 56 1 which is traced as follows. From the positive terminal of battery l 35 through leads I35 and I3? to switch left-E33, then through winding I6 1, lead 156i, switch IdS-ISS to lead IE6, and then back to the'ne'gative terminal of battery I35. Current flow through winding its causes armature I53 to be attractedtowards the electromagnet, and the pawl I58 is'therefore conditioned to adjust ratchet 59 in step should the armature I53 be released. The release of armature E63 takes place, because the carrier radiation at the transmitter is resumed after having been interrupted for one-tenth of a second by relay l thus causing the resumption of current flow in winding 97 after this period of time and independently of the next dialing operation.

Upon release of armature I53 the cam disc ISI is rotated an angular distance equal to one tooth of the ratchet I59, and this is sufficient to shift the connector plate I56 to contact 202 and its mate contact. It will be noted that simultaneously the cam follower rides out of recess ItZ thereby closing switch ITS-ll! and opening switch H2il3. The transfer to relay winding I has accordingly been accomplished, and the system is conditioned so that dialing of numeral '7 steps the connector plate 297 to its predetermined seven oclocl; position. That this will take place is readily seen from the fact that the relay winding 59$ is now in circuit with the battery I35 by virtue of the fact that the lead 2M connects back to the negative terminal of battery I35 through the same path described in connection with winding H5, except for the fact that the connector plate 556 now connects contact 262 and its mate to lead lei. As previously described in connection with the stepping of connector plate I88, the connector plate 201 will be adjusted to its desired position by virtue of the stepping of ratchet 2% an angular distance of seven teeth. The cam disc 2G5 will assume substantially the position hown in Fig. 4. The cam follower I95 will open switch -2IlI95 and close switch I95- 2W.

It will now be appreciated that connector plates 22! and 2 33 are adjusted in sequence in accordance with the same series of operations already described. It is not believed necessary to repeat the series of operations, since it has been previously pointed out that at the end of each dialing operation carrier radiation will be momentarily interrupted thereby closing switch let-I32 to permit flow of current from battery I35 through winding It l. This will result in the ratchet I59 being moved one tooth as soon as carrier radiation is resumed. Therefore, when numeral 9 isdialed the connector plate I55 has already been positioned over contact 2H5 and its mate contact.

Hence, the winding 2I3 is now in circuit with battery I35 by virtue of the lead 2I5 being connected to contact 2N5. As a result of dialing 9 the connector plate 221 will be adjustably positioned to contacts 222 and 223'. As soon as the carrier is interrupted after this dialing operation, the switch I33--I-32 is closed.- again and the pawl I53 is ready to move the ratchet another tooth. Before the dialing of the second numeral 9 the connector plate I56 has been moved to connect contact 236 and its mate contact thereby connecting lead 235 and winding 233 in circuit with battery I35. Thus dialing of the second numeral 9 will result in adjustment of connector plate 243 to the position where it connects contactsz i l' and 245. It will be noted that there is no companion contact associated with contact 248. Upon momentary interruption of the carrier and then resumption of carrier radiation after the passage of 7; of a secend, the connector plate I56 will be shifted into its final position where it electrically connects contacts 54 and I55. Upon this latter connection taking place the controlled circuit which 23 sistance. If it is impossible to obtain therequired time constant by this expedient, a simple relay might be used.

While we have indicated and described a preferred system for carrying our invention into effect, it will be apparent to one skilled in the art that our invention is by no means limited to the particular organizations shown and'described, but that many modifications may. be made without departing from the scope of our invention.

What we claim is:

1. A receiving system comprising at least one amplifier having an input circuit sharply tuned to a desired carrier wave, means for applying to said input circuit a double frequency modulated carrier wave, said input circuit deriving from said wave a corresponding amplitude modulated carrier wave wherein the modulation is in the form of a frequency modulated sub-carrier, a rectifier provided with an input connection to said amplifier for rectifying the amplitude modulated wave energy, a resonant load circuit connected to said rectifier and tuned to develop thereacross modulation voltage derived from said amplitude modulated wave energy, a second amplifier having at least one sharply tuned input circuit to which said modulation voltage is applied whereby there is produced an amplitude modulated wave whose modulation is the second harmonic of the original modulation on the carrier, means for rectifying the last mentioned amplitude modulated wave energy to produce an alternating current component and a direct current component, means for amplifying the alternating current component, and means responsive to said direct current component for controlling the effectiveness of the last mentioned amplifying means.

2. A receiving system comprising at least one amplifier having an input circuit sharply tuned to a desired carrier wave, means for applying to said input circuit a double angle modulated carrier wave,.said input circuit deriving from said wave a corresponding amplitude modulated carrier wave, a rectifier provided with an input connection to said amplifier for rectifying the amplitude modulated wave energy, a resonant load circuit connected to said rectifier and tuned to develop thereacross modulation voltage derived from said amplitude modulated wave energy, a second sharply tuned input circuit to which'said modulation voltage is applied whereby there is produced an amplitude modulated wave whose modulation is the second harmonic of the original modulation on the carrier, and means'for rectifying the last mentioned amplitude vmodulated wave energy.

3. In a frequency modulated wave receiver, a selective network tuned to the mean frequency of the wave and being adapted to produce from said modulated wave energy amplitude modulated wave energy whose modulation frequency is the double harmonic of the original modulation frequency applied to said wave, means for detecting said amplitude modulated wave to provide said double harmonic modulation, and a resonant modulation utilizing circuit tuned to said double harmonic frequency.

4. In a frequency modulated wave receiver, a selective network tuned to the mean frequency of the wave and being adapted to produce from said modulated wave energy amplitude modulated wave energy whose modulation frequency is the double harmonic of the original-modulation frequency applied to said wave, means-for detecting said amplitude modulated wave to pro vide said double harmonic modulation, a resonant modulation utilizing circuit tuned to said double harmonic frequency, and means responsive to the direct current voltage component of the detected wave voltage for rendering said utilizing circuit effective.

5. In a frequency modulated wave receiver, a selective network tuned to the mean frequency of the wave and being adapted to produce from said modulated wave energy amplitude modulated wave energy whose modulation frequency is the double harmonic of the original modulation frequency applied to said wave, means for detecting said amplitude modulated wave to provide said double harmonic modulation,a resonant modulation utilizing circuit tuned to said double harmonic frequency, a normally-open controlled circuit, means for closing said controlled circuit, and means'responsive to a predetermined number of pulses of current in said utilizing circuit for adjusting said closing means to circuit-closing position.

6. A frequency modulation receiver comprising a selective amplifier having at least one resonant circuit tuned to the mean frequency of received frequency modulated carrier waves, said resonant circuit having its constants chosen to render it operative to produce substantial translation of the wave energy into corresponding amplitude modulated wave energy of the same means frequency, means for rectifying said amplitude modulated wave energy, said rectifying means including a load impedance tuned to the frequency of the modulation on said translated wave energy, an amplifier for said modulation, said tuned impedance additionally being the in' put circuit of the last amplifier.

'7. In a modulated carrier wave receiver, a selective network tuned to the frequency of the wave and being adapted to produce from said modulated wave energy amplitude modulated wave energy whose modulation frequency is the double harmonic of the original modulation frequency applied to said wave, means for detecting said amplitude modulated wave to provide said double harmonic modulation, and a modulation utilizing circuit coupled to the detecting means.

8. In a frequency modulated wave receiver, a plurality of cascaded selective networks each tuned to the mean frequency of the wave and being adapted to derive from said modulated wave energy amplitude modulated wave energy whose modulation frequency is the double harmonic of the original modulation frequency applied to said wave, means for detecting said amplitude modulated wave to provide said double harmonic modulation, a modulation utilizing circuit, and means responsive to the direct current voltage component. of the detected wave voltage for controlling said utilizing circuit.

9. In an angle modulated carrier wave receiver, at least one selective network tuned to the mean frequency of thewave and being adapted to derive from said modulated carrier wave energy amplitude modulated wave energy whose modulation frequency is the double harmonic of the original modulation frequency applied .to said wave, means for detecting said amplitude modulated wave to provide said double harmonic modulation, a modulation utilizing circuit, a normally-open.controlled circuit, means for closing said controlled circuit, and means responsive to a predeterminednumber of pulses of current in 21' includes the leads 25'! is. completed, and the controlled device is actuated. In the instant case the controlled device is. a detonator.

Provision is made to home the dialing relays for the various situations which may occur. wherein receivers other than the desired receiver are partially actuated, or for the situation wherein the desired receiver is only partially actuated and the complete operation not carried out. It has. been previously pointed out that ifthe trans fer relay is released longer than the holding. time of the homing relay, the latter will: delay about two seconds and then release. If for any reason, therefore, the homing relay releases armature I42, it will be seen that switches Iii-I SI and let-4.43 are. opened. The filament circuits of the audio tubes are promptly opened. It is important to. note that the transfer relay should be the first to home. Otherwise it is possible that in the process of homing, one of the dialing connectors might sweep over and momentarily establish a firing circuit.

Release of armature G2 establishes a circuit through the buzzer contacts Ila-H59 of the transfer ratchet relay. The complete circuit is traced as follows: current source I35, lead 536, lead I31, switch I33-I32, lead 556, winding i 84,

lead I68, buzzer contacts I5-Ill, armature IE3,

contact III, follower I13, switch I4EIl3, lead I43 and back to current source I35. Closing this circuit permits current flow through winding IM, and armature IE3 is attracted. This breaks the contact between IEEIand I79, and armature I63 falls thereby steppin ratchet E59. Closure of contacts IfiQ-I'IG takes place again, and the ratchet I59 isstepped clockwise in this manner until the recess I62 of cam disc IQI receives convex portion I'M of follower I73. In this position the connector plate I55 is back to home or twelve oclock position, i. e., its normal posi tion. Further, the switch I'III'I3 is opened, while switch I 'I3Il2.is closed. Hence, the homing circuit through the transfer ratchet relay is broken, while a homing circuit has been estab-v lished through winding I by virtue of the following circuit: battery I 35, leads I35 and [37, winding I755, buzzer contacts III.-l9', armature I88, switch I92-I89, lead I953, switch I72- I13, switch M3Id6, lead Hi5 and back to battery I35.

The ratchet I82 is actuated as previously described for-ratchet I 59 until cam disc i 84 reaches normal position, wherein cam follower I89 is seated and switch I92I2.9 is opened. In this position the connectorunit is at its home or normal setting. 'Each of the following ratchets 2M, 2I8 and 235 may be sequentially actuated in the same manner. In each case the homing of a given cam disc transfers the homing circuit to the followin relay winding untilall the relay cams are at home or normal positions. It will now be seen that by causing the transfer ratchet relay to home before the following relays, there can never be an inadvertent completion ofthe controlled circuit by virtue ofonly three proper numbers being dialed and the fourth being dialed during the homing operation.

The condenser I53- across the dialing relay contacts increases the reliability of the dialing operation for Weak or short dialing pulses. Its function is to charge instantly when the dialing contacts I49 and I48 are first established, before the current through the winding I28 can build up due to its, self-inductance. Once condenser ['53 is. charged, however, it. will discharge. through the relay coils even though the. dialing contacts have opened. The condenser is made. as. large. as possible consistent with rapid dialing. The resistor I52 serves to limit the initial charging current to values that. preclude freezing of the contacts, but does. not greatly affect the charging time of the condenser.

I15, etc., associated with each of the dialing relay coils are spark absorbing capacitors to reduce reaction on the'receiver circuits. In the absence of such condensers the tuned receiver circuits might pick up pulseswhich would operate relays to transmit new pulses that would thus sustain an oscillating or motorboating system. It will. be obvious, ofcourse, that several four-figure numbers may be set up to establish several firing circuits leading to different mine fields.

In the absence, of a signal from the detonating transmitter severe noise may operate the transfer ratchet relay L64. For operation of. a, dialing ratchet. relay thefilaments of the audio.- amplifier tubes must be heated (due to closing. of the transfer sensitive relay), and further the antenna noise input must be of the order of severalvolts. Even if. the audio amplifier filaments are. heated, any noise impulse. sufficient to operate a dialin ratchet relay will be more than that required to'operatethe transfer ratchet relay I54. High amplitude noise of sufficient duration to actuate all of the dialingratchetv relays is unlikely. Completion. of the firingcircuit requires that each of the ratchets be advanced at. least one position so thatv chance detonation due to noise is remote.

At the cessation of. the noise the ratchets home to. the standby position. During the operation of the receiver by a. signal from the transmitter, noise impulses may. cause the trans fer relay ratchet to advance one or more steps in addition to those steps caused by the normal signals. The same impulses might also advance a dialing relay ratchet, but, in general, this requires more severe noise. If a single mine field contained 10,000 receivers with the same carrier, I. and audio frequencies, each receiver with a different dial combination, then any number dialed would. fire the corresponding mine. If in the process of dialing, a single noise pulse of just sufiicient amplitude to actuate the transfer ratchet relay occurred, a different or undesired combination would result and a different mine would'be fired.

The inclusion of a resistance and condenser time constant means 251' in the firing circuit prevents. noise or static, which occurs during the dialing. operation, from firing any mine other than that desired. This, however, does not insure that the desired mine will be fired. If noise causes an extra transfer operation, then the total number of transfer operations will be five rather than the normal of four. At the completion of the dialing operation the transfer relay ratchet will be in a position one beyond that which completes the firing. circuit. The time constant in thefiring circuit must be longer than the time taken to dial a single zero. This prevents firing during the time the transfer relay ratchet passes through the firing position. Obviously if the noise had not occurred during the dialing operation, the desired mine would be detonated by merely waiting the time required for the firing circuit current to build up. The time constant necessary to perform this function is of the order of one second. It-is possible that this time constant could be obtained by merely shunting the squib or detunator with a large capacity and adding seriesre- The shunt condensers, I65,

25 said utilizing circuit for adjusting said closing means to circuit-closing position.

10. In a system of radio control of the type wherein there is radiated a control Wave in the form of a carrier wave modulated by a sub-carrier which is in turn modulated by a plurality of successive groups of sequential audio pulses, and wherein the carrier wave is momentarily interrupted at the end of each of said groups; a receiver for said control Wave comprising means for deriving from the modulated carrier wave the said groups of modulation at the second harmonic frequency thereof, a controllable circuit including a plurality of circuit-closing devices arranged in series and which must be adjusted in a predetermined order corresponding to said group succession, means responsive to said carrier interruptions for determining said predetermined order, a plurality of actuating devices each respectively associated with a respective one of said circuit-closing devices, and means for energizing each of said actuating devices in accordance with a predetermined group of said audio pulses.

11. A frequency modulation receiver comprising a selective amplifier having at least one resonant circuit tuned to the mean frequency of received frequency modulated carrier waves, said resonant circuit having its constants chosen to render it operative to produce substantial translation of the Wave energy into corresponding am- 26 plified amplitude modulated wave energy of the same mean frequency, means for rectifying said amplitude modulated Wave energy, said rectifying means including a load circuit tuned to the frequency of the modulation on said translated amplified wave energy.

12. In a system of control of the type wherein there is employed a control Wave in the form of a carrier wave modulated by a sub-carrier which is in turn modulated by a plurality of successive groups of sequential audio pulses, and wherein the carrier wave is momentarily interrupted at the end of each of said groups, means for deriving from the modulated carrier wave the said groups of modulation at the second harmonic frequency thereof, a circuit including a plurality of circuit-closing devices arranged in series and which must be adjusted in a predetermined order corresponding to said group succession, means responsive to said carrier interruptions for determining said predetermined order, a plurality of actuating stepping devices each respectively associated with a respective one of said circuitclosing devices, and means for energizing each of said actuating devices in accordance with a predetermined group of said audio pulses.

HARMON B. DEAL. WHJLIAM R. ALEXANDER. JOHN A. RANKIN. 

